1. Field of the Invention
This invention concerns an open-celled cellulosic sponge containing a water-insoluble polymer capable of selectively removing dissolved ions from aqueous systems.
2. Description of the Prior Art
The use of ion exchange resins for the absorption of dissolved ions is well known. Such resins are generally manufactured in bead form and are utilized in columns through which liquids are passed to interact with the beads. The beads are generally made of cross-linked polystyrene which is then chemically modified. Two chemical modifications of such resins are prevalent, namely: a resin having sulfonic acid groups and capable of exchanging positively charged ions (cations), and a resin having quaternary ammonium groups and capable of exchanging negatively charged ions (anions). Except for their selectivity for either cations or anions, such resins do not generally distinguish between different kinds of cations or anions as may be found in multi-component solute mixtures.
An ion exchange resin attached to an open-celled cellulose sponge is described in U.S. Pat. No. 4,332,916. Because such product is self-supporting and of potentially large size, it can be confined in retention means other than columns, and is substantially unaffected by water-borne suspended matter. In view of its physical characteristics, it is eminently suited for the treatment of flowing natural waters where high flow volumes and high sediment levels are encountered. The ion exchange resin of U.S. Pat. No. 4,332,916 is essentially a cation exchange resin chemically bonded to the hydroxyl groups of the cellulose of the sponge by means of a cross linking agent. Such bonding is accomplished at the relatively low temperature of 110 degrees C.
U.S. patent application Ser. No. 395,535, filed Aug. 18, 1989 U.S. Pat. No. 5,002,984 discloses an insolubilized polyethyleneimine (PEI) polymer deposited in situ within an open celled cellulosic sponge. The insolubilized PEI is generated by initially forming a water solution of PEI and an insolubilizing co-reactant, applying said solution to a cellulosic sponge, drying the treated sponge to remove water of solution, then curing the sponge at temperatures in the range of 130 degrees C. to 165 degrees C. The resultant insolubilized PEI is found to exhibit a unique mode of function wherein ions are absorbed based upon formation of a coordination complex involving repeating ethyleneamine units of the PEI.
It has been found however, that the relatively high temperatures and prolonged heating times of 20 to 80 minutes required to produce the insolubilized PEI cause thermal decomposition and oxidative degradation of the polymer and cellulose. It has also been found that treated sponges generally have a high loading of polymer in the peripheral regions, but have little or no polymer in the center region of the sponge. When the usual corrective measures were explored to remedy said problems, the resultant sponges had an unacceptably low add-on of less than 15% of polymer. When sponges of said Patent Application, prepared in sizes determined by commercially available sizes of cellulosic sponges, were utilized as a column packing to treat water, deformation of the sponges occurred, producing excessive impedance of flow. Although the metal-laden sponges may be eluted and re-used, or disposed of by incineration, it is sometimes desirable to dispose of the sponges in other ways. It has been found that the sponges of relatively large size were difficult to elute or burn, and were not readily amenable to other disposal routes.
It is accordingly an object of the present invention to provide a water-treating product comprised of an open-celled cellulosic sponge containing insolubilized polyethylenemine.
It is a further object of this invention to provide a water-treating product as in the foregoing object wherein said insolubilized polyethyleneimine is substantially uniformly distributed throughout the sponge.
It is a another object of the present invention to provide a product of the aforesaid nature which can be employed in a column configuration without undergoing deformation with attendant causation of increased impedance to flow of water.
It is a still further object of this invention to provide a product of the aforesaid nature having a content of insolubilized polyethyleneimine of at least 15%.
It is yet another object of the present invention to provide a product of the aforesaid nature readily amenable to disposal by compression techniques
These objects and other objects and advantages of the invention will be apparent from the following description.